Redshifted and thermally bistable one-way quantitative hemithioindigo-derived photoswitches enabled by isomer-specific excited state intramolecular proton transfer.

We report bistable indole-containing hemithioindigos (HTIs) with one-way quantitative photoswitching properties. Supported by state-averaged CASPT2/CASSCF calculations, we propose a mechanism for the observed one-way photoswitching that involves an isomer-specific excited state intramolecular proton transfer (ESIPT). Additionally, we developed a thermally bistable oligomer-inspired bipyrrole-containing HTI, which displays large band separation and bidirectional near-quantitative photoisomerization in the near-infrared, bio-optical window.

Simulating the solvation structure of low- and high-spin [Fe(bpy)]: long-range dispersion and many-body effects.

When characterizing transition metal complexes and their functionalities, the importance of including the solvent as an active participant is becoming more and more apparent. Whereas many studies have evaluated long-range dispersion effects inside organic molecules and organometallics, less is known about their role in solvation. Here, we have analysed the components within solute-solvent and solvent-solvent interactions of one of the most studied iron-based photoswitch model systems, in two spin states.

Taming the Complexity of Donor-Acceptor Stenhouse Adducts: Infrared Motion Pictures of the Complete Switching Pathway.

Switches that can be actively steered by external stimuli along multiple pathways at the molecular level are the basis for next-generation responsive material systems. The operation of commonly employed molecular photoswitches revolves around one key structural coordinate. Photoswitches with functionalities that depend on and can be addressed along multiple coordinates would offer novel means to tailor and control their behavior and performance.

Photoprogramming Allostery in Human Serum Albumin.

Developing strategies to interfere with allosteric interactions in proteins not only promises to deepen our understanding of vital cellular processes but also allows their regulation using external triggers. Light is particularly attractive as a trigger being spatiotemporally selective and compatible with the physiological environment. Here, we engineered a hybrid protein in which irradiation with light opens a new allosteric communication route that is not inherent to the natural system.

Crystal Field in Rare-Earth Complexes: From Electrostatics to Bonding.

The flexibility of first-principles (ab initio) calculations with the SO-CASSCF (complete active space self-consistent field theory with a treatment of the spin-orbit (SO) coupling by state interaction) method is used to quantify the electrostatic and covalent contributions to crystal field parameters. Two types of systems are chosen for illustration: 1) The ionic and experimentally well-characterized PrCl crystal; this study permits a revisitation of the partition of contributions proposed in the early days of crystal field theory; and 2) a series of sandwich molecules [Ln(η -C H ) ] , with Ln=Dy, Ho, Er, and Tm and n=5, 6, and 8, in which the interaction between Ln and the aromatic ligands is more difficult to describe within an electrostatic approach. It is shown that a model with three layers of charges reproduces the electrostatic field generated by the ligands and that the covalency plays a qualitative role.

Introducing QMC/MMpol: Quantum Monte Carlo in Polarizable Force Fields for Excited States.

We present for the first time a quantum mechanics/molecular mechanics scheme which combines quantum Monte Carlo with the reaction field of classical polarizable dipoles (QMC/MMpol). In our approach, the optimal dipoles are self-consistently generated at the variational Monte Carlo level and then used to include environmental effects in diffusion Monte Carlo. We investigate the performance of this hybrid model in describing the vertical excitation energies of prototypical small molecules solvated in water, namely, methylenecyclopropene and s-trans acrolein.

Multiple-Resonance Local Wave Functions for Accurate Excited States in Quantum Monte Carlo.

We introduce a novel class of local multideterminant Jastrow-Slater wave functions for the efficient and accurate treatment of excited states in quantum Monte Carlo. The wave function is expanded as a linear combination of excitations built from multiple sets of localized orbitals that correspond to the bonding patterns of the different Lewis resonance structures of the molecule. We capitalize on the concept of orbital domains of local coupled-cluster methods, which is here applied to the active space to select the orbitals to correlate and construct the important transitions.